Modern fire control systems contain components which form one of the following three categories of subsystems: the aiming system, the fire control computer, and the sensors. The aiming system performs the task of precisely establishing the ballistic angles of elevation and azimuth for the boresight of a gunnery weapon such as a tank relative to the line of sight to the target.
The ballistic angles are computed by a fire control computer in accordance with information which it receives from the gunner and from the various sensors installed on the tank. They depend on the type of projectile being fired, range to the target, wind direction, relative velocity between the tank and the target, and other factors.
The quality of the fire control systems currently available is primarily dependent on the precision of the aiming systems in static firing, that is, where a stationary tank is firing upon a stationary target. Improved fire control systems coming into use allow for firing on the move, and also against moving targets. These systems are very costly, as exemplified by the systems found on the American M1 tank and German Leopard 2 tank.
The firing capability on the move is obtained by the use of aiming systems providing a stabilized line-of-sight. Stabilization of the light of sight permits the gunner to observe a steady and clear landscape without disturbance from rolling and dipping due to motion, to identify the target, to aim at the target with high precision, and to accomplish firing with a high hit probability. Addition of autotracking to these systems further expands their capabilities as it enables precision aiming at moving targets, such as helicopters, despite rapid shifting of the line of sight.
Existing technology in the area of stabilized sights uses biaxial deflection of the head mirror of the gunner's sight in relation to the body of the sight which is rigidly attached to the tank turret. Control of this deflection is achieved by a biaxial platform located in the sight and inertially stabilized with the aid of rate sensors.
The angles of elevation and azimuth of the tank gun relative to the line of sight are measured by three precision angular sensors. One of these is located on the gun trunnion and measures the elevation of the gun relative to the turret. The other two are located in the sight and measure the elevation and azimuth angles of the line-of-sight through the gunner's sight relative to the turret.
The line-of-sight is independently stabilized and is under the control of the gunner. The gun is slaved to the line-of-sight through its servo positioning loops by the determined ballistic angles which are newly defined for each shot by the fire control computer. The servo positioning loops are closed by the three angular sensors.
Because of the high inertia of the gun, it cannot be slaved to the stabilized line-of-sight with sufficient precision to accomplish firing. Thus, the firing is achieved by a technique in which control of firing by the gunner is accomplished only when the actual angle of the gun approaches the calculated ballistic angle within a predetermined zone. That is, the gunner's trigger command is inhibited until the boresight angle is within a predetermined "window". This technique limits the ultimate accuracy of such fire control systems.